Contribution of amplitude modulations for concurrent stream segregation: A probe through object-related negativity

Auditory streaming based on amplitude modulations (AMs) might be responsible for concurrent vowel identification and F0 difference limen for high pass filtered harmonics. However, no clear evidence is available for the contribution of AM in concurrent stream segregation. This study aimed to investigate the role of high rate AM in concurrent stream segregation using a behavioral task and object-related negativity (ORN). Ten adults aged 18-25 years participated in the study. Three participants coherently or incoherently modulated narrow band noises with the bandwidth of 1 ERBN were presented for a perceptual stream segregation task, as well as for eliciting ORN. In the incoherent condition, the middle band was modulated at 1, 2, and 4 semitones higher than 120 Hz and other two bands were modulated at 120 Hz. In the coherent condition, all three bands were modulated at the same rate. It was expected that the incoherently modulated stimuli would produce the perception of two streams, whereas coherently modulated stimulus would produce single stream perception. The d-prime analysis revealed that listeners had low sensitivity to stream segregation even at 4 semitone differences and d-prime was not significantly different from 0. Similarly, differences in AM did not elicit ORN. The results of this study suggest that differences in AM up to 4 semitones do not lead to concurrent stream segregation.